Question

I have one now.numsSet, inside the elements are as follows:

\> db.nums.find()
 { "_id" : ObjectId("599c3f530686a4fe90ef5a6f"), "n" : 1 }
 { "_id" : ObjectId("599c3f530686a4fe90ef5a70"), "n" : 2 }

Define a query document and find all documents with n not equal to 5:

> var query={n:{$ne:5}}

Then try usingfindFunction query:

> db.nums.find(query)
 { "_id" : ObjectId("599c3f530686a4fe90ef5a6f"), "n" : 1 }
 { "_id" : ObjectId("599c3f530686a4fe90ef5a70"), "n" : 2 }

It is normal to find out that there are two results.
But then I want to change all the n that meet the requirements to 5, and use it according to my idea.$neYou should be able to filter out two results so that the N of both documents should be 5, but:

> db.nums.update(query,{$set:{n:5}})
 WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
 > db.nums.find()
 { "_id" : ObjectId("599c3f530686a4fe90ef5a6f"), "n" : 5 }
 { "_id" : ObjectId("599c3f530686a4fe90ef5a70"), "n" : 2 }

It seems that only the first n is changed to 5, while the second one is not, but the second one is also satisfied.queryWhat are the query criteria for?
Update can only change the first result?

Answer 1

Read the document carefully.updateIn the history of the method, only one document is modified by default. If you want to modify multiple documents that meet the criteria, you should use parameters.{multi: true}:

> db.nums.update(query,{$set:{n:5}}, {multi: true});

Later, in order to prevent confusion, it was addedupdateOne/updateManyMethod, so it can also be written as:

> db.nums.updateMany(query,{$set:{n:5}});